Method of manufacturing an optical connector

ABSTRACT

The invention is directed to a method of manufacturing an optical connector according to which it is possible to adjust a projection length a bare optical fiber (7) projects from a connection end surface (3) of a ferrule (1). At a step (a), an optical fiber cored line (5) is inserted through and attached to an optical fiber insertion hole (4) of the ferrule (1), and the bare optical fiber (7) and the ferrule (1) are bonded to each other by hardening a heat-hardening adhesive (11) at a first hardening temperature. Next, at a step (b), the connection end surface (3) is ground so that the connection end surface (3) becomes flat and flush with a tip surface of the bare optical fiber (7). Following this, at a step (c), the heat-hardening adhesive (11) is heated again to be hardened at a temperature which is higher than the first hardening temperature, so that a tip of the bare optical fiber (7), causing pistoning due to the reheat hardening, projects from the connection end surface (3). The quantity of the projection is adjusted by controlling one or both of the rehardening temperature and a holding time at the rehardening temperature.

TECHNICAL FIELD

The present invention is related to a method of manufacturing an opticalconnector in which a connection tip of an optical fiber projects alittle longer from a connection end surface of the optical connector.

BACKGROUND ART

A conventional optical connector is obtained by forming an optical fiberinsertion hole which penetrates between a rear end of a ferrule and aconnection end surface which is a front end of the ferrule, thereafterinserting an optical fiber through the optical fiber insertion hole fromthe rear end side toward a tip, thereafter fixedly bonding the opticalfiber and the ferrule using a heat-hardening adhesive which contains anepoxy or the like, and thereafter grinding the connection end surfacetogether with a tip surface of the optical fiber.

When this type of optical connectors are to be connected to each other,connection end surfaces of one optical connector and the other opticalconnector are abutted against each other after aligning the opticalconnectors to each other in such a manner that an optical fiber of oneoptical connector is abutted against an optical fiber of the otheroptical connector without any positional displacement, whereby theoptical fibers are connected to each other through the connectors.

Since connection of optical fibers to each other using this type ofoptical connectors is a method of connecting optical fibers to eachother which requires to abut connection end surfaces of the opticalconnectors against each other, if a small gap is created between theoptical fiber of one of the optical connectors and the optical fiber ofthe other one of the optical connectors, reflection of light or the likeis created at the gap, which increases a connection loss. To deal withthis, when optical connectors are to be connected to each other, amatching agent (matching oil) is applied to connection end surfaces ofthe optical connectors so that an inconvenience such as reflection oflight is prevented when the optical connectors are connected to eachother.

However, applying a matching agent every time optical connectors areconnected to each other is very much burdensome, and therefore, it isimpossible to enhance the operability of connecting optical connectorsto each other. Against the backdrop, recent years have seen an increaseduse of optical connectors of a physical contact type which allowsoptical fibers to be connected to each other without using a matchingagent. An optical connector of the physical contact type is manufacturedby grinding a connection end surface of a ferrule using a buff afterinserting an optical fiber through the ferrule and fixing the opticalfiber therein. Buff grinding is performed utilizing a fact that theferrule whose hardness is small is chipped off more than the opticalfiber whose hardness is large, thereby allowing the optical fiber toproject a little longer from the connection end surface of the ferrule.

When optical fibers are to be connected to each other using opticalconnectors of the physical contact type, connection end surfaces of theconnectors are abutted against each other and the optical fibers of theoptical connectors which project a little longer from the connection endsurfaces are accordingly brought into a direct pressure contact witheach other so that reflection of light or the like at this contactportion is prevented, which in turn makes it possible to connect theoptical fibers to each other without using a matching agent and hencewith only a small connection loss.

An optical connector mounting an optical fiber cored line may containonly one line. However, with a recent tendency toward opticalcommunication with a large capacity, a ferrule mounting containing morethan one optical fibers of cable conductors is in a popular use.

During fabrication of a multi-cored optical connector of the physicalcontact type, in particular, when a connection end surface of a ferrulein which multi-cored optical fibers are arranged is ground using a buffin an effort to allow tips of the optical fibers to project from the endsurface of the ferrule as conventionally performed, since the buff issoft, as it is known in the art, the buff chips off different quantitiesat different positions, so that the multi-cored optical fibers areground away different quantities and projection lengths of the opticalfibers accordingly become different from each other. This degrades theperformance of connecting the multi-cored optical fibers and makes itimpossible to perform reliable connection of the optical fibers.

The present invention has been made to solve such a problem.Accordingly, an object of the present invention is to obtain a method ofmanufacturing an optical connector which, even if an optical connectoris a multi-cored optical connector, allows optical fibers eachcontaining a cored-line to project evenly from a connection end surfaceand adjusts the projection so that the quantities of the projection areoptimum.

DISCLOSURE OF THE INVENTION

The present invention uses the following means to achieve the objectabove. That is, in a first aspect of the invention, means for solvingthe problem is a structure in which an optical fiber is inserted througha fiber insertion hole which opens at a connection end surface of aferrule, a heat-hardening adhesive is thereafter injected between theferrule and the optical fiber, the heat-hardening adhesive is thereafterhardened in an atmosphere at a first hardening temperature, theconnection end surface of the ferrule is thereafter ground together withan end surface of the optical fiber so that the surfaces become flatwith each other, and an integrated and bonded unit of the ferrule andthe optical fiber as they are bonded to each other are thereafter keptin an atmosphere at a rehardening temperature which is higher than thefirst hardening temperature so that a tip of the optical fiber projectsfrom the connection end surface of the ferrule.

In a second aspect of the invention, means for solving the problem is astructure which comprises the structure according to the first aspectand in which a projection length the tip of the optical fiber projectsfrom the connection end surface of the ferrule is adjusted bycontrolling at least one of the rehardening temperature and a holdingtime at the rehardening temperature.

In a third aspect of the invention, means for solving the problem is astructure which comprises the structure according to the first or thesecond aspect and in which the rehardening temperature is higher than aglass-transition temperature of the heat-hardening adhesive which isobtained at the first hardening temperature.

In the invention with such a structure as above, the optical fiber isinserted through the ferrule, and after hardening using theheat-hardening adhesive in an atmosphere at the first hardeningtemperature, the connection end surface of the ferrule is ground so thatthe connection end surface of the ferrule and a tip surface of theoptical fiber become flat and flush with each other.

Next, in an initial stage of rehardening the integrated and bonded unitof the ferrule and the optical fiber in an atmosphere at the rehardeningtemperature, as the rehardening temperature is higher than the firsthardening temperature, the optical fiber which is inserted through andfixed to the ferrule causes a phenomenon called pistoning andaccordingly projects from the connection end surface of the ferrule.When the rehardening temperature is higher than a glass-transitiontemperature T_(g) of the heat-hardening adhesive which is obtained atthe first hardening temperature, in particular, as a heating temperatureexceeds the glass-transition temperature T_(g), the heat-hardeningadhesive becomes a rubber-like state, a Young's modulus of theheat-hardening adhesive drops to about 1/3, and a holding power of theoptical fiber becomes small, so that the optical fiber projects in alarger quantity. The quantity of the projection is adjusted by therehardening temperature and a holding time in the atmosphere at therehardening temperature.

In short, the higher the rehardening temperature is, or the longer theholding time in the atmosphere at the rehardening temperature is, themore the optical fiber projects.

The projection length the optical fiber projects from the connection endsurface of the ferrule is adjusted by controlling one or both of therehardening temperature and the holding time in the atmosphere at therehardening temperature. Therefore, even if an optical connector is amulti-cored optical connector, projection lengths optical fibers ofcable conductors project are adjusted to be uniform.

The present invention requires that after hardening an optical fiberwhich is inserted through a ferrule using the heat-hardening adhesive atthe first hardening temperature, the connection end surface of theferrule is ground so that the connection end surface of the ferrule andthe tip surface of the optical fiber become flat and flush with eachother, and that the projection length the optical fiber projects fromthe connection end surface of the ferrule is adjusted by controlling oneor both of the rehardening temperature and the holding time at therehardening temperature, and therefore, it is possible to solve theproblem of uneven projection lengths of optical fibers which isassociated with conventional buff grinding for setting the projectionlengths of the optical fibers, and to set the projection lengths of theoptical fibers proper as designed. Further, since it is possible toadjust the projection lengths of the optical fibers equal to each other,it is possible to perform reliable connection of optical fibers usingoptical connectors of the physical contact type which are manufacturedby the method according to the present invention, to connect the opticalfibers through the connectors with a small loss, and to enhance thereliability of the connection of the optical fibers.

In addition, since reheat hardening is executed at the rehardeningtemperature which is higher than the glass-transition temperature of theheat-hardening adhesive which is obtained at the first hardeningtemperature, during the reheat hardening, the heat-hardening adhesivereaches the glass-transition temperature and the holding power of theoptical fiber is accordingly weakened, and therefore, the optical fiberprojects more. Thus, it is possible to adjust the projection length ofthe optical fiber in an efficient manner. Further, since the reheathardening is performed at the rehardening temperature which is higherthan the glass-transition temperature of the heat-hardening adhesivewhich is determined by the first hardening temperature, it is possibleto increase the glass-transition temperature of the heat-hardeningadhesive in accordance with the reheating temperature. When therehardening temperature is set higher than a temperature at which theoptical connector is to be used, in particular, the glass-transitiontemperature of the heat-hardening adhesive is set higher than thetemperature at which the optical connector is to be used, and hence,while the optical connector is used, the heat-hardening adhesive reachesthe glass-transition temperature and accordingly weakens the holdingpower. This prevents a phenomenon that the optical fiber projects againdue to pistoning and the projection length of the optical fiberaccordingly changes, and therefore, enhances the reliability of theoptical connector over a long term.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) to 1(d) are explanatory diagrams of a preferred embodiment,showing steps of a method of manufacturing an optical connectoraccording to the present invention;

FIGS. 2(a) to 2(c) are views showing a projection length of an opticalfiber which is measured using a surface roughness meter, after ground ata rehardening temperature of 90° C., after reheat hardening and afterapplication of heat shock; and

FIGS. 3(a) to 3(c) are views showing a projection length of an opticalfiber which is measured using a surface roughness meter, after ground ata rehardening temperature of 100° C., after reheat hardening and afterapplication of heat shock.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in detail with reference to theassociated drawings. FIGS. 1(a) to 1(d) show steps of a method ofmanufacturing an optical connector according to a preferred embodimentof the present invention. In FIGS. 1(a) to 1(d), a ferrule 1 is formedusing an epoxy resin, and an optical fiber insertion hole 4 is formedpenetrating from a rear end surface 2 of the ferrule and a connectionend surface 3 which is a front end surface of the ferrule. At a tip endof the optical fiber insertion hole 4, an optical fiber cable conductor5 is inserted in such a manner that a bare optical fiber 7 with a sheath6 removed projects from the connection end surface 3 of the ferrule 1.At a base end of the optical fiber insertion hole 4, the sheath 6 of theoptical fiber cored line 5 is inserted in the optical fiber insertionhole 4.

A boot 8 is fit between the optical fiber cored line 5 and the opticalfiber insertion hole 4 at the rear end of the ferrule, if necessary. Anopening width in a vertical direction of the base end side of theoptical fiber insertion hole 4 at the rear end is larger than a diameterof a hole through which the bare optical fiber 7 is inserted at the tipof the optical fiber insertion hole 4.

If the optical fiber cored line 5 is multi-cored, a corresponding numberof bare optical fibers 7 which corresponds to the number of cores areinserted through and arranged in the ferrule 1.

In the ferrule 1, an adhesive injecting hole 10 is formed in the middleof the optical fiber insertion hole 4, in such a manner that theadhesive injecting hole 10 is linked to the optical fiber insertion hole4. At the step shown in FIG. 1(a), the optical fiber cored line 5 isinserted through the optical fiber insertion hole 4 of the ferrule 1 tosuch a position which allows the bare optical fiber 7 to project fromthe connection end surface 3 of the ferrule 1 through the optical fiberinsertion hole 4, and in this condition, a heat-hardening adhesive 11containing an epoxy is injected through the adhesive injecting hole 10.The heat-hardening adhesive 11 flows into the optical fiber insertionhole 4 and fills up a gap between the bare optical fiber 7 and theoptical fiber insertion hole 4.

After injecting the heat-hardening adhesive 11, the ferrule 1 is placedin a heating furnace with the heat-hardening adhesive 11 injected. Atemperature within the heating furnace is kept at a first hardeningtemperature for hardening the heat-hardening adhesive 11. The ferrule 1is held within the furnace for a predetermined period of time, tothereby harden the heat-hardening adhesive.

At the first step for hardening the heat-hardening adhesive, the firsthardening temperature is set low, a holding time for holding within thefurnace is set short, and the glass-transition temperature T_(g) of theheat-hardening adhesive 11 is set low.

When cooled under a certain condition from a liquid state, a polymermaterial including the heat-hardening adhesive freezes into a glassstate after becoming a supercooled liquid. Such a transition from asupercooled liquid into a glass state without crystallization is calledglass transition, and a temperature of the glass transition is calledthe glass-transition temperature T_(g). The heat-hardening adhesive of ahardened state, when heated up from a room temperature, changes from theglass state into a rubber-like elastic state at the glass-transitiontemperature T_(g). The heat-hardening adhesive have largely differentproperties before and after reaching the glass-transition temperatureT_(g). For example, as the heated heat-hardening adhesive exceeds theglass-transition temperature T_(g), the resin softens, and hence, thebonding strength remarkably degrades and the coefficient of linearthermal expansion increases double or triple.

While the initial glass-transition temperature T_(g) of theheat-hardening adhesive is determined by the initial hardeningtemperature (i.e., the first hardening temperature) and the holding timeat the initial hardening temperature, the glass-transition temperatureis also related to a crosslinking density of the heat-hardeningadhesive. Therefore, as heating for rehardening is performed at atemperature which is higher than the glass-transition temperature whichis determined by the initial heating for hardening, the glass-transitiontemperature changes to a value which corresponds to the reheatingtemperature and a holding time at the reheating temperature. Thepreferred embodiment utilizes such a change in the glass-transitiontemperature.

FIG. 1(b) shows a step of performing grinding. As described earlier,grinding is executed after connecting and fixing the optical fiber coredline 5 to the ferrule 1 using the heat-hardening adhesive 11. Thegrinding does not use a buff as customarily performed in theconventional technique, but uses a grinding board made of a grind stoneor tape grinding as that proposed in Japanese Patent Application No.Hei-8-29911 which was filed by the applicant of the present application,to thereby grind the connection end surface 3 of the ferrule 1 and a tipsurface of the bare optical fiber 7 so that the surfaces become flat andflush with each other.

Following this, after this grinding, the ferrule 1 with the opticalfiber cored line 5 fixed thereto is placed in the heating furnace andrehardening is performed by heating the heat-hardening adhesive 11 onceagain. FIG. 1(c) shows a step of the reheat hardening. The rehardeningtemperature within the heating furnace during the reheat hardening isset higher than the first hardening temperature which is used at thestep of FIG. 1(a), and a holding time in an atmosphere at therehardening temperature is set longer. In the preferred embodiment,heating is performed at a temperature which is higher than theglass-transition temperature T_(g) of the heat-hardening adhesive 11which is determined by the first hardening temperature which is used atthe step of FIG. 1(a) and the holding time at the first hardeningtemperature.

During the heating at the rehardening temperature, heated at atemperature which is higher than the glass-transition temperature, theheat-hardening adhesive 11 becomes a rubber state, the Young's modulusof the heat-hardening adhesive drops to about 1/3, and an adhesionholding power of the optical fiber (i.e., the bare optical fiber 7)decreases. This causes pistoning of the bare optical fiber 7, so thatthe optical fiber projects from the connection end surface 3 of theferrule 1. The quantity of the projection the optical fiber projects isadjusted by controlling one or both of the rehardening temperature andthe holding time in the atmosphere at the rehardening temperature. Inother words, the rehardening temperature is increased and the holdingtime at the rehardening temperature is extended if the quantity of theprojection is to be large. For controlling the projection length of theoptical fiber in this manner, experiments are conducted in advance toobtain data regarding a relationship between the rehardening temperatureand the quantity of the projection of the optical fiber during theassociated holding time. By controlling the rehardening temperature andthe associated holding time in accordance with the data, it is possibleto obtain a designed projection length of the optical fiber.

After allowing the optical fiber to project in this manner, theatmosphere at this temperature is maintained as shown in FIG. 1(d), sothat a crosslinking density of the heat-hardening adhesive 11 changes.This changes the glass-transition temperature of the heat-hardeningadhesive 11 to a higher temperature, the Young's modulus of theheat-hardening adhesive 11 increases, and the holding power of the bareoptical fiber accordingly increases. After rehardening theheat-hardening adhesive 11 at the rehardening temperature in thismanner, the ferrule with the optical fiber projecting is taken out fromthe heating furnace, thereby completing fabrication of the desiredoptical connector.

According to the preferred embodiment, the connection end surface 3 isground and flattened after connecting and fixing the optical fiber,which is inserted through the optical fiber insertion hole 4 of theferrule 1, at the first hardening temperature, and the ferrulecomprising the ground optical fiber cored line conductor is heated onceagain while controlling the rehardening temperature of the reheating andthe corresponding heating time, and hence, it is possible to allow theoptical fiber to project uniformly a desired length from the connectionend surface 3 of the ferrule 1. This allows optical fibers of opticalconnectors to abut with each other in a proper pressure contact when theoptical connectors are to be connected to each other, and therefore, itis possible to achieve excellent connection using the connectors withonly a small connection loss and enhance the reliability of theconnection of the optical fibers through the connectors.

Further, since the reheat hardening is performed at the rehardeningtemperature which is higher than the glass-transition temperature of theheat-hardening adhesive 11 which is determined by the first hardeningtemperature and the holding time in the atmosphere at the firsthardening temperature, it is possible to increase the glass-transitiontemperature of the heat-hardening adhesive 11. When the rehardeningtemperature is set higher than a temperature at which the opticalconnector is to be used, in particular, it is possible to increase theglass-transition temperature of the heat-hardening adhesive 11sufficiently higher than the temperature at which the optical connectoris used.

Thus, by setting the glass-transition temperature of the heat-hardeningadhesive 11 higher than the temperature at which the optical connectoris to be used, it is possible to prevent without fail a problem of adeteriorated holding power of the optical fiber upon reach of theheat-hardening adhesive 11 to the glass-transition temperature while theoptical connector is used, and hence, it is possible to ensure thereliability of the optical connector over a long term. Further, sincethe glass-transition temperature of the heat-hardening adhesive 11 isset higher than the temperature at which the optical connector is to beused, the heat-hardening adhesive 11 never reaches the glass-transitiontemperature while the optical connector is used, and therefore, it ispossible to prevent pistoning and an associated further projection ofthe optical fiber during use of the optical connector. Hence, it ispossible to sufficiently enhance the reliability of the opticalconnector.

Now, a specific example of the method of manufacturing an opticalconnector according to the present invention will be described. Theexample requires to perform similar steps to those of the preferredembodiment which is shown in FIGS. 1(a) to 1(d), to thereby manufacturean optical connector. More specifically, after inserting the opticalfiber cored line 5 through the optical fiber insertion hole 4 of theferrule 1 and injecting the heat-hardening adhesive 11 which contains anepoxy through the adhesive injecting hole 10, the heat-hardeningadhesive 11 was hardened in a heating furnace for one hour at the firsthardening temperature of 60° C. After the heat-hardening adhesive 11 washardened at the first hardening temperature, the glass-transitiontemperature T_(g) of the heat-hardening adhesive 11 was 40 to 50° C.

Next, the grinding step was performed as shown in FIG. 1(b) so that theconnection end surface 3 of the ferrule 1 and the tip surface of thebare optical fiber 7 were ground to be flat and flush with each other.The quantity of the projection of the optical fiber after the grindingwas then measured using a surface roughness meter. The measured quantityof the projection the optical fiber projects was 0.3 to 0.4 μm. A causeof the projection of the optical fiber despite the grinding of theconnection end surface 3 of the ferrule 1 and the tip surface of thebare optical fiber 7 so that the surfaces would be flush with each otheris considered to be a difference in the ground quantities between thematerial of the ferrule and the glass material of the optical fiber dueto a difference between the hardness of the material of the ferrule andthe hardness of the glass material of the optical fiber.

In this example, the experiments were conducted using different samples,and the ground samples were divided into two groups. For one group, theheat-hardening adhesive 11 was heated again for rehardening at therehardening temperature of 90° C. for the holding time of one hour. Forthe other group, the heat-hardening adhesive 11 was heated again forrehardening at the rehardening temperature of 100° C. for the holdingtime of one hour. The glass-transition temperature of the heat-hardeningadhesive 11 after the reheat hardening was 80 to 90° C. for the firstgroup which was subjected to the reheat hardening at 90° C. for onehour, but was 100 to 110° C. for the second group which was subjected tothe reheat hardening at 100° C. for one hour. Thus, it was proved thatthe glass-transition temperature of the heat-hardening adhesive 11 canbe increased by setting the rehardening temperature high.

Next, the projection lengths of the optical fibers from the connectionend surface after the reheat hardening of the heat-hardening adhesive 11were measured using a surface roughness meter. As a result, thequantities of the projection of the optical fibers after the reheathardening at 90° C. for one hour were 0.6 to 0.9 μm, while thequantities of the projection of the optical fibers after the reheathardening at 100° C. for one hour were 1.0 to 1.3 μm. Thus, it wasproved that the projection lengths of the optical fibers can beincreased by setting the rehardening temperature high.

Next, after the reheat hardening of the heat-hardening adhesive 11, thesamples of the respective groups were placed in the heating furnace onceagain, kept at 80° C. for one hour, and subjected to heat shock, and theprojection lengths cf the optical fibers were measured again using asurface roughness meter. The projection lengths of the optical fibers ofthe first group after application of the heat shock were 0.6 to 0.9 μm,while the projection lengths of the optical fibers of the second groupwere 1.0 to 1.3 μm. Thus, a change in the projection length of theoptical fiber due to the heat shock was not observed. This is becausethe heat shock was applied at a temperature which is lower than theglass-transition temperature of the heat-hardening adhesive after thereheat hardening. In other words, even when heat shock is applied at atemperature which is lower than the glass-transition temperature of theheat-hardening adhesive 11 which is determined by the rehardeningtemperature, the optical fiber does not project further. It then followsthat it was proved that by setting the glass-transition temperature ofthe heat-hardening adhesive 11 which is determined by the rehardeningtemperature higher than a temperature at which the optical connector isto be used, it is possible to prevent a change in the projection lengthof the optical fiber due to the temperature at which the opticalconnector is used. Table 1 shows measured projection lengths of theoptical fibers as they were after the grinding, after the reheathardening and after application of the heat shock.

                  TABLE 1                                                         ______________________________________                                                   Rehardening Temperature                                            Step         90° C. (one hour)                                                                  100° C. (one hour)                            ______________________________________                                        After ground 0.3 ˜ 0.4 μm                                                                     0.3 ˜ 0.4 μm                                  After reheat hardening 0.6 ˜ 0.9 μm 1.0 ˜ 1.3 μm                                    After heat shock 0.6 ˜ 0.9 μm 1.0                                   ˜ 1.3 μm                                    ______________________________________                                    

Further, FIGS. 2(a) to 2(c) and 3(a) to 3(c) show examples of measuredprojection lengths of the optical fibers which were taken using asurface roughness meter. FIGS. 2(a) to 2(c) show the measurements forthe first group which was subjected to the reheat hardening at 90° C.,while FIGS. 3(a) to 3(c) show the measurements for the second groupwhich was subjected to the reheat hardening at 100° C. Among FIGS. 2(a)to 2(c) and 3(a) to 3(c), FIGS. 2(a) and 3(a) show the measurementsafter the grinding, FIGS. 2(b) and 3(b) show the measurements after thereheat hardening, and FIGS. 2(c) and 3(c) show the measurements afterthe heat shock at 80° C. for one hour. The examples of the measurementsshown in FIGS. 2(a) to 2(c) and 3(a) to 3(c) represent an exampleregarding a multi-cored connector each containing eight cores.

While the example above requires to change the rehardening temperatureand keep the holding time at the rehardening temperature constant,another experiment was conducted with a constant rehardening temperaturewhile changing the holding time at the rehardening temperature. From theexperiment, it was confirmed that the projection lengths of the opticalfibers were increased by extending the holding time.

Hence, it is possible to freely adjust the projection lengths of theoptical fibers either by controlling the rehardening temperaturevariable, controlling the holding time at the rehardening temperaturevariable, or controlling both the rehardening temperature and theholding time at the rehardening temperature.

The present invention is not limited to the embodiment and examplesdescribed above. Rather, various embodiments of the present inventionare possible. For example, although the embodiment and examplesdescribed above require to perform heating for rehardening only once,the heating for rehardening may be performed twice or more times. Inthis case, the glass-transition temperature may be gradually increased,such that a reheating temperature for the first time is higher than theglass-transition temperature which is determined by the first hardeningtemperature but a reheating temperature for the second time is higherthan the glass-transition temperature which is determined by thereheating temperature which was used for the first reheating.

INDUSTRIAL APPLICABILITY

As described above, the method of manufacturing an optical connectoraccording to the present invention is appropriate for manufacturing ofan optical connector of a one-cored or a multi-cored type in which a tipof an optical fiber projects a little longer from a connection endsurface of a ferrule.

What is claimed is:
 1. A method of manufacturing an optical connector,the method comprises the following sequence of steps:inserting anoptical fiber through a fiber insertion hole of a ferrule, the opticalfiber protruding from a connection end surface of the ferrule; injectinga heat-hardening adhesive between the ferrule and the optical fiber;heating the heat-hardening adhesive to a first hardening temperature toharden the adhesive; grinding the connection end surface of the ferruleand the protruding end surface of the optical fiber so that the surfacesbecome flush with each other to form an integrated and bonded unit ofthe ferrule and the optical fiber; heating the integrated and bondedunit of the ferrule and the optical fiber to a rehardening temperaturewhich is higher than the first hardening temperature and higher than theglass-transition temperature of the heat-hardening adhesive, so that atip of the optical fiber projects from the connection end surface of theferrule.
 2. The method of manufacturing an optical connector accordingto claim 1, wherein a projection length the tip of the optical fiberprojects from the connection end surface of the ferrule is adjusted bycontrolling at least one of the rehardening temperature and a holdingtime at the rehardening temperature.